Dry Hutt River causing concern
Wellington’s main water source – the Hutt River – is running at near-record low flows, prompting one expert to question whether more water can be used to supply the cities.
Ecologist Dr Mike Joy, one of New Zealand’s leading freshwater experts, wants residents to think about the impact they are having on the Te Awa Kairangi/Hutt River every time they clean their car or water their lawn.
The river provides drinking water for about 400,000 residents across the region. At its current low levels, he said it was unrealistic for Wellington Water to keep taking more and more water.
“[Wellington Water] should not be taking so much water out of it. There should be meters and we should not be using beautiful clean drinking water to wash cars.”
Joy is also angered so much water is lost to leaks and said the way to make Wellingtonians understand value of the resource was to make them pay for it.
In recent years toxic algae has become an increasing problem in the river and that pointed to bigger issues, he said.
Oxygen levels in the river fluctuate when the water is low and, unlike introduced fish, native species cannot cope with lower levels of oxygen and quickly die if water quality is poor.
There has been only one major rain event in the last few months, before a downpour overnight, and Joy said that would also be affecting water quality.
Downpours “flush” the river of algae and generally improve water quality.
As of 10.10am on May 1, the river at Taita Gorge was flowing at 3.07 cubic metres per second (c³/s). That is roughly four and a half times lower than the corresponding time last year.
According to Land Air Water Aotearoa, the flow was 2.2 c³/s in March 1985, at the height of a significant drought. During heavy rain on April 13, it reached 62.6 c³/s.
Greater Wellington water resilience monitoring lead Braden Crocker said it had been a lengthy dry spell.
For 95% of the time since records started, the river has been flowing at a higher level.
MetService forecaster James Millward said the region has experienced El Nino conditions since Christmas, with little rain.
The prevailing south westerly winds had “stripped the moisture out of the ground” and there had been little rain in the Tararua Range, where most of the water originates.
Although there had been two days of heavy rain in April, the rest of the month had seen little rain.
It would take sustained rain to fill rivers and although some heavy rain was forecast for this week, Millward said the next month was likely to see a continuation of dry weather. There was “more variability” expected from the end of May.
Niwa forecaster Ben Noll predicted May would be “drier than normal” and with the region having experienced a long dry spell, Wellington needed sustained rain.
With the weather cooling in autumn, most people assumed the need to reduce water use was a thing of the past.
The region, however, remains under level two restrictions, with Wellington Water continuing to urge locals to observe water restrictions, including not using sprinklers.
When river levels are low, Wellington Water takes water from its backup supply, Te Marua Lakes in Upper Hutt.
Network operations manager Jeremy McKibbin said the summer “has had a long tail”, with river levels falling well into autumn. This had made level two water restrictions necessary for longer than previous years.
“Low river levels reduce the amount of water we can take, which then increases reliance on the aquifer and the storage lakes,” he said. “Water restrictions play a key role here in reducing the risk of demand outpacing supply or suddenly spiking.”